Performance of MLI Seams between 293 K and 20 K Wesley Johnson and David Chato Fluid and Cryogenic Systems Branch, Glenn Research Center 2019 Cryogenic Engineering Conference

Fundamental Approach for Developing Multilayer Insulation MLI Blankets Traditional SS-MLI IMLI Hybrid

Fundamental Approach for Developing Multilayer Insulation Penetration Integration: NASA-TP-2012-216315 Seams MLI Blankets - Traditional SS-MLI IMLI Hybrid

Fundamental Approach for Developing Multilayer Insulation Skirt Integration Penetration Integration: NASA-TP-2012-216315 Seams Repeatability MLI Blankets - Traditional SS-MLI IMLI Hybrid By accounting for each item separately, LOX ZBO testing accurately predicted total MLI performance. More information is needed for SHIIVER. Tape, Pins & Attachments

Introduction Performance is lost in multilayer insulation systems due to joints and seams in the insulation blankets: Recognized as a concern since the introduction of multilayer insulation. Insulating large tanks more seams required as the tank dimensions exceed the roll widths available Over the years mitigation techniques have been developed: These include overlapping every layer, or precision cutting to minimize the gap However labor intensive and time consuming. Shu investigated “cracks” in MLI in early 90s at liquid nitrogen temperatures Recently Fesmire and Johnson re-examined the seams issue with a liquid nitrogen test rig at KSC and confirmed many of the previous findings. This effort extends the seams work into liquid hydrogen temperatures and studies a broader range of proposed seam configurations.

Calorimeter Description

Test Matrix Test Number Description MLI Layers Seam Construction Offset, x, (in) 1 Overlap seam 50 1 stagger 2 Interleaved Seam N/A 3 Butt seam Straight 4 5 6 20 7 Overlap Seam 8 Butt Seam 9

Blanket Descriptions Feature Yetispace Existing Blankets Number of layers (total) 20 50 Number of sub-blankets 2 Number of layers per sub-blanket 10 25 Reflector Substrate Polyester Reflector Deposited Metal Aluminum Reflector thickness 0.00635 mm (0.25 mil) # spacers thicknesses per reflector Spacer Material Dacron B2A Spacer Thickness 0.1778 mm Covers thickness 5 mil Design Sub-blanket Thickness 0.42 cm 1.59 cm Design layer density 24 lay/cm 16 lay/cm

Typical Test Results (1/2)

Typical Test Results (2/2)

50 Layer Test Results Overlapped seams out performed butt seams Offsetting butt seams didn’t seem to provide any benefit By the time the butt seam is handled, radiation path becomes torturous Minimal difference between the best and worst seams Test Number Run Qtotal, watts Tavg, K Kavg, W/m/K DT, K Qnet, W dQ, W dQ, W/m 1 Overlap Seams 0.788 21.06 29.8 2.56 0.786 0.040 0.044 2 Interleaved 0.748 19.16 27.3 2.43 0.746 0.000  3 Full Butt 0.806 18.85 26.9 2.51 0.802 0.056 0.061 4 Butt 2" Offset 2.52 0.803 0.057 0.062 5 Butt 4" Offset 0.810 19.37 27.8 0.807 0.067

20 Layer Seam Results Once again, Overlap seam out performed butt seam. Minimal heat gains into system Offsetting butt seams didn’t provide any benefit Much bigger difference between the best and worst seaming configurations Test Number Run Qtotal, watts Tavg, K Kavg, W/m/K DT, K Qnet, W dQ, W dQ, W/m 6 Interleaved 1.033 20.38 28.9 3.49 1.012 0.000 7 Overlap 1.035 18.62 26.6 3.65 1.015 0.003 8 Butt 2" Offset 1.222 17.52 25.0 4.21 1.199 0.187 0.205 9 Full Butt 1.160 17.25 24.7 4.09 1.146 0.134 0.147

Conclusions Measured heat loads for the nine tests conducted. Layer by layer interleaved joint showed the lowest heat leak. Overlap joint out performed the straight and staggered butt joints. Surprisingly staggering the butt joint did not decrease the heat load Increasing the stagger distance didn’t help. In fact the test with the largest stagger was worse than straight butt joint, (although this may be due to damage incurred by repeated handling rather the joint itself). Technician installed by “stitch taping” joints every ~5 layers, may have shown that stitch taping is as good as full taping Even worst performing seam only 5% more heat leak than best performing seam at 50 layers There are significant differences between 20 layers and 50 layers. This shows that the impact of seams is reduced with increased numbers of layers.

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